Straight wing type wind and water turbine

ABSTRACT

A Straight blade type turbine has at least one two-dimensional blade positioned in parallel with and around a central axis of the turbine. The two-dimensional blade has a cross section with a blade cord turned around a center of the two-dimensional blade by an angle of 3° to −2° relative to a line perpendicular to another imaginary line connecting the central axis with the center of the two-dimensional blade. A distance between a fore end and the center of the cross section is 15 to 40 percent of a cord length of the blade. NC/R, which is calculated by a radius R extending from the axis to the center of two-dimensional blade, the cord length C, and the number N of the two-dimensional blades, is between 0.5 and 2.2. A maximum thickness of the two-dimensional blade is between 20 and 25 percent of the cord length. The turbine has a strut blade having a symmetric cross section joining the two-dimensional blade to a side of the central axis, the strut blade having a maximum thickness which is between 15 and 20 percent of a cord length of the strut blade.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a straight blade type turbinehaving a plurality of straight blades each disposed around a verticalaxis and connected to a side of the vertical axis by a strut blade. Thestraight blade has a cross section with a solidity, a direction angle, athickness, etc. which improves the turbine in an operational efficiency,an easy self start, and a less noise.

[0003] 2. Related Art

[0004] Recently, a wind power generation and a water power generationhave been reevaluated in view of a less energy consumption and anational environment conservation.

[0005] Regarding a wind power generation, a wind turbine having apropeller with a horizontal axis has been mainly used. A propeller windturbine has a better self starting performance without a specifiedstarting device but has a directivity relative to a wind direction.Thus, the wind turbine requires a device which faces the wind turbineagainst a wind. Furthermore, the propeller has disadvantageously acomplicated profile which is difficult in a mass production thereof.

[0006] Furthermore, some wind turbines having a vertical axis and aplurality of vertically elongated blades have been utilized. A famousone of them is a Darrieus wind turbine which has a plurality ofelongated blades with an arc profile around a vertical shaft.

[0007] A vertical axis wind turbine has no directivity against a winddirection so that it is suitable for a wind varying in seasons like inJapan. In addition, the vertical axis wind turbine has a simplifiedblade profile and is easy for a mass production thereof. The verticalaxis wind turbine has an operational efficiency (output coefficient)equal to that of a horizontal axis wind turbine. Herein, the efficiencyrepresents a ratio of an output (a torque multiplied by a rotationalnumber) to an energy of a wind. Regarding a vertical axis water turbineused in a water power generation, the efficiency represents a ratio ofan output of the water turbine to an energy of a water.

[0008] However, the conventional vertical axis wind turbinedisadvantageously has an extremely low self start performance, whichrequires various kinds of equipment such as a starting motor and adevice for controlling the motor. Thereby, the vertical axis windturbine requires such equipment increased in size and cost although ithas blades simplified in the profile. Furthermore, the vertical axiswind turbine needs to have an improved profile of the blades to obtain ahigher efficiency (output coefficient). The vertical axis wind turbinehas a larger acoustic noise which must be overcome. These problems alsoappear in a water turbine.

SUMMARY OF THE INVENTION

[0009] In view of the above mentioned situation, an object of theinvention is to provide a turbine having a vertical axis generally,which achieves a better operational efficiency (output coefficient).Preferably, the turbine has abetter self starting performance without aspecial starting device and is quiet when rotated.

[0010] For achieving the object, a straight blade type turbine describedin claim 1 according to the present invention, which has at least onetwo-dimensional blade positioned in parallel with and around a centralaxis of the turbine, characterized in that

[0011] the two-dimensional blade has a cross section with a cord lengthturned around a center of the two-dimensional blade by an angle of 3° to−2° relative to a line perpendicular to another imaginary lineconnecting the central axis with the center of the two-dimensionalblade;

[0012] a distance between a fore end and the center of the cross sectionis 15 to 40 percent of the cord length;

[0013] NC/R, which is calculated by a radius R extending from the axisto the center of two-dimensional blade, the cord length C, and thenumber N of the two-dimensional blades, is between 0.5 and 2.2; and

[0014] a maximum thickness of the two-dimensional blade is between 20and 25 percent of the cord length.

[0015] In this configuration, when the turned angle of thetwo-dimensional blade is not less than 5°, the turbine has anoperational efficiency (output coefficient) is zero not to serve as aturbine. Meanwhile, the turned angle of 3° to −2° can provide at least ahalf of a maximum efficiency (output coefficient) of the turbine toobtain a better efficiency of the rotating turbine. When a distancebetween a fore end and the center of the cross section is 15 to 40percent of the cord length, a better efficiency of the turbine isobtained, so that ahead falling moment of the straight blade keeps aself starting performance of the turbine, although the efficiency ismaximum at the mounting position where the distance is 25 percent of thecord length. Furthermore, NC/R (solidity or blade area ratio) not lessthan 0.5 provides a better self starting performance, while the soliditymore than 2.2 decreases in the efficiency (output coefficient). Thus,NC/R of 0.5 to 2.2 maintains an appropriate efficiency as well as anadequate self starting performance of the turbine. Moreover, a maximumthickness of the two-dimensional blade, which is between 20 and 25percent of the cord length, improves the turbine in the self startingperformance and the efficiency of the turbine with keeping a sufficientstrength of the two-dimensional blade. Accordingly, the turbine isbetter in the self starting performance and the efficiency thereof.

[0016] A straight blade type turbine described in claim 2 is dependenton claim 1, characterized in that the turbine comprises a strut bladehaving a symmetric cross section joining the two-dimensional blade to aside of the central axis, the strut blade having a maximum thicknesswhich is between 15 and 20 percent of a cord length of the strut blade.

[0017] This configuration provides a low rotational resistance of thestrut blade and maintains a sufficient strength of the two-dimensionalblade, further improving the turbine in the self starting performance.

[0018] A Straight blade type turbine described in claim 3 has at leastone two-dimensional blade positioned in parallel with and around acentral axis of the turbine, characterized in that the two-dimensionalblade has a cross section provided with a stream line convex having athickness which is substantially a half of a maximum thickness of thetwo-dimensional blade.

[0019] This configuration decrease air eddies generated in a rear sideof the two-dimensional blade when used in a wind turbine, decreasing ordiminishing an acoustic noise of the two-dimensional blade. Likewise,the configuration decreases water eddies generated in a rear side of thetwo-dimensional blade when used in a water turbine, decreasing ordiminishing the noise due to the two-dimensional blade.

[0020] A straight blade type turbine described in claim 4 is dependenton claim 3, characterized in that the stream line convex has a thicknesswhich is between 12 and 17 percent of a cord length of the strut blade.The configuration diminishes an air or water noise generated by therotation of two-dimensional blade.

[0021] A turbine described in claim 5 is dependent on claim 1 or 2,characterized in that the two-dimensional blade has the stream lineconvex described in claim 3 or 4.

[0022] This configuration includes the turned angle of 3° to −20° theposition of the center of the cross section of 15 to 40 percent of thecord length, the NC/R determined between 0.5 and 2.2, the thickness ofthe two-dimensional blade being between 20 and 25 percent of the cordlength, and has the cross section provided with a stream line convex.This achieves the turbine better in the self starting performance andthe efficiency (output coefficient) thereof and decreases or diminishesan air or water noise thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a perspective view showing an embodiment of a straightblade type turbine according to the present invention;

[0024]FIG. 2 is a sectional view taken along line A-A of FIG. 1 forshowing a section profile of a straight blade;

[0025]FIG. 3 is a sectional view taken along line B-B of FIG. 1 forshowing a section profile of a strut blade;

[0026]FIGS. 4A, 4B, and 4C are explanatory views showing the straightblade, the blade angle being zero in FIG. 4A, plus in FIG. 4B, plus inFIG. 4C;

[0027]FIG. 5 is a graph showing a relationship between the blade angleand an efficiency (output coefficient) of the turbine;

[0028]FIG. 6 is a graph showing a relationship between the blade centerand an efficiency of the turbine;

[0029]FIG. 7 is a graph showing a relationship between a solidity (NC/R)and an efficiency of the turbine, which includes curves each related toeach blade angle;

[0030]FIG. 8 is a graph showing a relationship between a solidity and anefficiency of a turbine having another straight blade;

[0031]FIG. 9 is a graph showing a relationship between a tip speed ratioand an efficiency of a turbine, which includes curves each related toeach solidity;

[0032]FIG. 10 is a graph showing a relationship between a solidity andan efficiency of a turbine based on FIG. 9, which includes curves eachrelated to each tip speed ratio; and

[0033]FIGS. 11A, 11B, and 11C are sequentially a top view, a front view,and a side view of a stream line convex located at an end of thestraight blade.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] Referring to the accompanied drawings, embodiments of theinvention will be discussed in detail hereinafter.

[0035]FIG. 1 shows a straight blade type turbine having a vertical axis,which is an embodiment of the invention. The straight blade type turbine1 has a vertical shaft 2, a plurality (three in this embodiment) of mainstraight blades 3, and a plurality of horizontal strut blade 4 eachjoining each straight blade 3 to the shaft 2.

[0036] As illustrated in FIG. 2 which is a sectional view (hatchings areomitted) taken along line A-A of FIG. 1, the straight blade 3 is anasymmetric two-dimensional blade. The straight blade 3 has a mean line 9which is downwardly (downwardly in FIG. 2 and inwardly toward the shaftin FIG. 1) curved from a fore edge 7 and crosses a blade cord line 11 ata center 10 where the thickness of the two-dimensional blade is themaximum. The mean line 9 is curved upward from the center 10 to a rearedge 8 thereof. The strut blade 4 is arranged from the straight blade 3downward in FIG. 2. This profile of the two-dimensional bladeaccomplishes a higher efficiency (output coefficient) of the turbinewithout changing the angle of the two-dimensional blade in response to awind (water) direction. The profile of the straight blade 3 was proposedby the applicant of the present invention in Japanese Patent PublicationNO. 56-42751.

[0037] As illustrated in FIG. 3a which is a sectional view taken alongline B-B of FIG. 1, the strut blade 4 has a symmetric profile and acenter line aligned with a mean line 15 from a fore edge 12 to a rearedge 13 thereof. The symmetric strut blade 4 decreases in a resistantforce due to an air or wind stream at the fore edge 12, while thesymmetric strut blade 4 increases in a resistant force due to an air orwind stream at the rear edge 13, providing a rotational force for theturbine.

[0038] When the strut blade 4 adopts an asymmetric blade having asectional profile like the one of FIG. 2, an upper (FIG. 1) blade has asectional profile the same as the one of FIG. 2 while a lower (FIG. 1)blade has a sectional profile obtained by turning upside down the one ofFIG. 2.

[0039] Thereby, the upper two-dimensional blade generates a lift whichis cancelled by a downward force generated by the lower two-dimensionalblade, enabling a smooth rotation of the turbine Furthermore, a trustforce exerted on a bearing (not shown) of the shaft 2 decrease toimprove a useful life of the bearing.

[0040] Preferably, the straight blade 3 and the strut blade 4 are madeintegrally of a light weight and high strength material such as a glassfiber and a carbon fiber. The turbine 1 can be used as a wind turbine ora water turbine. The blade has a high rigidity, which can resist againsta strong water stream. The integrated body has no connection notches,which surely prevents the intrusion of water into the inside of theturbine. Furthermore, the light weight blade improves the turbine in aself starting performance and an efficiency (output coefficient)thereof.

[0041] Preferably, the shaft 2 is a hollow rotor shaft (2) made of ametal and has an end, for example, coupled to a rotational shaft of agenerator (not shown). The hollow rotor shaft decrease the shaft 2 inweight, improving a starting performance of the turbine. The straightblade 3 maybe a symmetric blade (symmetric section blade) where a windor water direction is constant so that a blade angle may not be varied.A circular plate (not shown) may be fitted to each of top and bottomportions of the blades 3 and a center of each plate may be supported toeliminate the shaft 2.

[0042] The efficiency (output coefficient) of the turbine 1 varies withthe blade angle of the straight blade 3 relative to the strut blade 4,the joining position of the straight blade 3 relative to the center ofthe shaft 2, the solidity of the turbine 1, etc. Also, the self startingperformance varies with the solidity of the turbine 1, the thickness ofthe straight blade 3 and the strut blade 4, etc.

[0043] As illustrated in FIG. 4A, an imaginary line 22 radiallyextending from a center 20 of the shaft 2 is perpendicular to animaginary line 22 of the straight blade 3 and crosses the imaginary-line22 at point 21. A ratio (%) of a distance X from the fore edge 7 of thestraight blade 3 to the cross point 21 relative to a cord length Crepresents the blade center position. As illustrated in FIGS. 4A, 4B,and 4C, the blade angle is indicated by an angle A (°) between a line 18and a blade cord line 11, where the line 18 is perpendicular to theradial imaginary line and the blade cord line 11 inclines inward oroutward relative to the line 18. FIG. 4B shows a blade angle of +á whileFIG. 4C shows a blade angle of −á, and FIG. 4A shows a blade angle of0°.

[0044] The solidity is defined by NC/R, which is calculated by a radiusR (meter) extending from the shaft center 20 to the cross point 22, thecord length C (meter), and the number N of the two-dimensional blades. Ablade thickness value is represented by a ratio (%) of a maximumthickness of the blade to the cord length. The efficiency (outputcoefficient) is a ratio of a work (torque multiplied by a rotationalspeed of the turbine) to an energy (defined as 1) of a wind or a water.

[0045] An object of the invention is to provide a turbine having avertical axis, which achieves a better self starting performance and abetter operational efficiency (output coefficient) by finding a best oreffectively used range regarding the functions such as the blade angle,the blade center, the solidity, and the blade thickness. Hereinafter, aresearch result with an analysis thereof regarding the factors will bediscussed.

[0046] First, a research result regarding the blade angle and theefficiency (output coefficient) is shown in a graph of FIG. 5. In FIG.5, a vertical coordinate indicates an efficiency and a horizontalcoordinate indicates a blade angle (°), while solidities (NC/R) wereselected sequentially between 0.18 and 4.0, which were five (0.18, 1.08,2.0, 3.0, and 4.0).

[0047] As understood from the FIG. 5, the efficiency of the turbinevaries greatly with the blade angles. A blade angle between +4° and −4°or at most between +5° and −5° is practical while the solidities werewithin an extremely large range from 0.18 to 4.0. A blade angle morethan +4° or less than −4°, or at most more than +5° or less than −5° isunpractical because a maximum efficiency of the turbine is almost zero.For obtaining a better efficiency (for example, more than 0.1) in FIG.5, a blade angle between +2° and −2° or at most between +3° and −3° canbe selected. A blade angle between +2° and −2° enables an efficiency(output coefficient) more than a half of a maximum (0.25 in FIG. 5). Ablade angle between +1° and −1° is best.

[0048] In FIG. 5, a maximum efficiency is obtained at a blade angle of+1° when the solidity is 0.18. When the solidity is between 1.08 and4.0, a maximum efficiency is obtained between 0° and +1°. Generally, ahigher efficiency is obtained at a blade angle of +1° than −1°, at ablade angle of +2° than −2°, or at a blade angle of +3° than −3°. Thatis, a plus blade angle provides an efficiency higher than a minus bladeangle as a whole. This tendency appears in a wind turbine as well as awater turbine.

[0049] Next, referring to FIG. 6, a research result regarding the bladecenter and the efficiency (output coefficient) will be discussed. InFIG. 6, a vertical coordinate indicates an efficiency and a horizontalcoordinate indicates a blade center (%), while the solidity (NC/R) isrepresented by a single value of 0.18. For example, the radius of theturbine is 1.25 meter and the cord length C is 0.3 meter.

[0050] In FIG. 6, a maximum efficiency (0.235) is obtained at a bladecenter of 25%. A relatively stable efficiency (output coefficient)between 0.118 and 0.079 is obtained when the blade center is positionedbetween 0% and 50%.

[0051] When the blade center is 0%, a line radially extended from theshaft (that is, along the strut blade) aligns with the fore end of thestraight blade in FIG. 4A. When the blade center is 50%, a line radiallyextended from the shaft crosses the blade cord line at the middle of thecord length. In FIG. 6, a most preferable blade center is 25%, while aline radially extended from the shaft crosses the cord length at aquarter of the cord length from the fore end of the straight blade inFIG. 4A.

[0052] A preferable blade center is positioned within a comparativelywide range of 0% to 50% in FIG. 6. However, a head falling moment (aforce exerted by the fore end of the straight blade toward the shaft) ofthe straight blade does not work effectively around the blade center of0%. Thus, a blade center more than 15% is practical to keep a preferableself starting performance. For obtaining an efficiency more than 0.1,the blade center is determined not within 50% but within 40%. This, adesirable blade center is selected between 15% and 40%. The tendency ofFIG. 6 appears in a wind turbine as well as a water turbine.

[0053]FIG. 7 is a graph showing a relationship between the solidity andthe efficiency, which is rewritten from FIG. 5. In FIG. 7, a verticalcoordinate indicates an efficiency (output efficiency) and a horizontalcoordinate indicates a solidity (NC/R), while the blade angles are 0°,+1°, +2°, +3°, −1°, −2°, and −3°.

[0054] As illustrated in FIG. 7, a larger solidity provides a smallerefficiency, which is a known matter. The efficiencies at a blade angleof 0° are almost the same as those at a blade angle of +1°. Theefficiencies at a blade angle of +2° are approximately equal to those ata blade angle of −1° . The efficiencies at a blade angle of +3° areapproximately equal to those at a blade angle of −2°. The efficienciesat a blade angle of −3° are greatly reduced to become lower than 0.1.From FIG. 7, it is noted that a blade angle is preferably selectedbetween +3° and −2°, while a solidity is selected between 0.18 and 4.0.

[0055] Practically, the solidity of 3 or 4 can not be selected. Forexample, a turbine having a solidity of the straight blade 3 includes adiameter of 0.3 meter and three straight blades with a 0.3 meter cordlength. This configuration is almost unpractical. A larger soliditydecreases a wind or water stream entering the turbine (in an inner spaceof the straight blades 3) to decrease a flow speed thereof, reducing therotation speed and torque of the turbine. Thus, a solidity around 2 is apractical upper limit because each curve of FIG. 7 becomes to have agentle slope there. A more practical upper limit of the solidity is 1 or1+α (α is preferably around 0.2) in consideration of the blade anglesincluding −3°.

[0056] A larger solidity provides a better self starting performance (aknown matter). The solidity should have a lower limit larger than 0.18in view of the self starting performance. The lower limit should beselected between 0.18 and 1, preferably around 0.6. An analysis of thesolidity will be discussed later. The tendency of FIG. 7 appears in awind turbine as well as a water turbine.

[0057] A part of original data corresponding to FIGS. 5 to 7 is shownfor reference in Table 1. TABLE 1 Tip speed ratio β Blade center Bladeangle at efficiency peak (%) (°) Efficiency (for reference)  0 3.430.118 2.6 10 2.06 0.203 ↑ 20 0.69 0.233 ↑ 25 0 0.235 ↑ 30 −0.69 0.227 ↑40 −2.06 0.171 ↑ 50 −3.43 0.079 ↑

[0058] The tip speed ratio described in Table 1 is a ratio of arotational speed of the straight blade at its fore end to a wind orwater stream speed. The tip speed ratio of 2.6 means that the straightblade moves 2.6 times of a wind or water stream speed. The efficiency ofthe turbine varies greatly with the tip speed ratio which will bediscussed later.

[0059]FIG. 8 is a graph showing a relationship between the solidity andthe efficiency (output coefficient) while the solidity extends from anextremely small value less than 0.1 to 3.5.

[0060] In that case, the straight blade has a comparatively thinsymmetric blade (NACA0012) having a blade thickness of 12%.

[0061] As understood from FIG. 8, a solidity of 0.1 corresponds to anefficiency more than 0.1. A curve of the efficiency rises up sharply tohave a peak around a solidity of 0.35. The efficiency decrease rapidlywhere the solidity varies from 0.35 to 0.65, and the efficiencydecreases gently where the solidity varies from 0.65 to 2.2. Theefficiency is almost constant where the solidity is around 2.2 andfurther decreases where the solidity increases from 2.4.

[0062] From an analysis of FIG. 8, it is understood that a betterefficiency of the turbine is obtained where the solidity is determinedbetween 0.1 and 0.65. Meanwhile, a better starting performance of theturbine is obtained where the solidity is determined between 0.65 and2.2 although the efficiency becomes lower.

[0063] An efficiency maximum Cp_(max) varies with a Reynolds number Reand a blade profile (section profile). C_(pmax) varies between 0.2 and0.48. The Reynolds number related to FIG. 8 is 1.33×10⁵. The efficiencyvaries also with the tip speed ratio of the straight blade. The tendencyof FIG. 8 appears in a wind turbine as well as a water turbine.

[0064]FIG. 9 is a graph showing a relationship between the tip speedratio and the efficiency (output coefficient) while the solidity issequentially selected from 0.36, 0.6, 1.2, 1.4, 1.6, 1.8, and 2.2. Aswell understood from FIG. 9, the efficiency increases when the tip speedratio increases, that is, when a ratio of the rotation speed of thestraight blade to a wind or water stream speed increases. A less tipspeed ratio β corresponds to a larger solidity while a larger tip speedratio corresponds to a less solidity. The tendency of FIG. 9 appears ina wind turbine as well as a water turbine.

[0065]FIG. 10 is a graph showing a relationship between the solidity andthe efficiency, which is rewritten from FIG. 9. In FIG. 10, a verticalcoordinate indicates an efficiency and a horizontal coordinate indicatesa solidity, while the tip speed ratios are four of 1.9, 2.0, 2.5, and3.0.

[0066] As well understood from FIG. 10, a larger tip speed ratio β (2.5or 3.0) provides a maximum efficiency within a less solidity range,while a less tip speed ratio β (1.9 or 2.0) provides a maximumefficiency within a larger solidity range.

[0067] Thus, a faster rotation of the turbine requires a less soliditythereof, while a slower rotation of the turbine requires a largersolidity thereof. From an analysis of FIG. 10, it is understood that thesolidity is determined to be more than 0.6, preferably between 0.6 and1.2, or between 0.6 and 2.2 to achieve a better starting performance. Alarger solidity and a less tip speed ratio are advantageous for a safetyof the turbine such as a dynamic strength and a fatigue strength. Thetendency of FIG. 10 appears in a wind turbine as well as a waterturbine.

[0068] The performance of the straight blade type turbine is representedby characteristic equations described hereinafter.

[0069] Speed reduction ratio a=½{1−{square root}{square root over ()}(1−Cfx)}

V _(R)=(1−a){square root}{square root over ( )}(1−2β sin φ+β²)$\begin{matrix}\begin{matrix}\begin{matrix}{{{Resistance}\quad {coefficient}\quad C_{fx}} = {{- \left( {{{nl}_{B}/4}\pi} \right)}{\int_{0}^{2}{\pi \quad V_{R}^{2}\quad \left\{ \left( {{C_{L}\cos \quad \varphi} + {C_{D}\sin \quad \varphi}} \right) \right.}}}} \\{\left. {{\cos \quad \varphi} + {\left( {{C_{D}\cos \quad \varphi} - {C_{L}\sin \quad \varphi}} \right)\sin \quad \varphi}} \right\} {\varphi}}\end{matrix} \\{C_{TB} = {\left( {{{nls}/4}\pi} \right){\int_{0}^{2}{\pi \quad {V_{R}^{2}\left( {{C_{L}\sin \quad \varphi} - {C_{D}\cos \quad \varphi} - {C_{M}l_{B}}} \right)}\quad {\varphi}}}}}\end{matrix} \\{{{Efficiency}\quad C_{p}} = {\beta \times C_{TB}}}\end{matrix}$

[0070] Where ls: Cord Length C_(B)/Radius R

[0071] V_(R): Wind or Water Speed (relative to blades)

[0072] φ: Turned Angle of Turbine

[0073] φ: Stream Attack Angle

[0074] C_(L): Lift Coefficient

[0075] Co: Resistance Coefficient

[0076] C_(M): Moment Coefficient

[0077] Table 2 shows, for reference, an analysis result obtained fromexperiments and calculations to generally indicate a relationship amonga solidity, a self starting performance, and an efficiency of theturbine. TABLE 2 Starting Tip Speed Ratio NC/R Performance EfficiencyC_(p) at efficiency peak 0.1 unacceptable small large 0.2 unacceptablemiddle large 0.3 unacceptable large 3.9 0.4 unacceptable large 3.4 0.5acceptable middle 3.0 0.6 acceptable middle 2.9 0.7 acceptable middle2.6 0.8 acceptable small 2.5 1.0 good small 2.3 1.2 good small 2.1 1.4good small 2.0 1.6 good small small 1.8 good small small 2.0 good smallsmall 2.2 good small small 2.4 good small small

[0078] In Table 2, a first column shows solidities; a second columnshows starting performances; a third column shows efficiencies; and aforth column shows tip speed ratios at efficiency peaks. From ananalysis of Table 2, the solidity is preferably selected between 0.5 and0.8 to obtain an appropriate starting performance and an adequateefficiency which allow an acceptable electric generating performance.

[0079] A most appropriate value of the solidity is around 0.7 in view ofa low tip speed ratio enabling an enough strength of the turbine, inwhich the starting performance is middle and the efficiency is middlewhile the tip speed ratio is a lower value. Even a solidity between 0.8and 2.2 may be selected since the efficiency decreases a little asillustrated in FIGS. 7 and 8. The tendency of Table 2 appears in a windturbine as well as a water turbine.

[0080] The starting performance and the efficiency are effected by athickness T (see FIG. 4A) of the straight blade and a thickness of thestrut blade as well as the solidity that is a blade area ratiodetermined by a radius R of the turbine, the number N of the straightblades, and a cord length C. An analysis of the thickness of thestraight blade and the strut blade will be discussed hereinafter.

[0081] Table 3 shows an analysis of a relationship of a thickness of thestraight blade (main blade) with a self starting performance, anefficiency, and a strength of the turbine, which is obtained fromexperiments and calculations thereof. TABLE 3 Blade thickness Starting(%) performance Efficiency Strength  5 unacceptable unaccetableunaccetable 10 unacceptable unaccetable unaccetable 15 acceptableacceptable acceptable 20 good good good 25 good good good 30 acceptableacceptable good 35 unacceptable unacceptable good 40 unacceptableunacceptable good

[0082] In Table 3, the blade thickness is represented by a ratio(percent) of a maximum blade thickness to a cord length C. As wellunderstood from Table 3, a blade thickness selected between 20% and 25%is most appropriate where the starting performance, the efficiency, andthe strength of the turbine are acceptable. A practical blade thicknessmay be selected between 15% and 30%. A blade thickness of 30% is betterthan a blade thickness of 15% in the starting performance althougheither of the thicknesses are acceptable in the starting performance.

[0083] A larger blade thickness selected between 35% and 40% increases arigidity of the straight blade but increases also the straight blade inweight. The increased weight is disadvantageous to keep a mechanicalstrength of the turbine during the rotation of the turbine. The strengthof the straight blade may be acceptable when the blade thickness is 30%and may be unacceptable when the blade thickness is between 35% and 40%.Therefore, the straight blade has tobe made of a fiber material having alighter weight with a higher strength such as a glass fiber and a carbonfiber. The fiber material may have a thickness around 2 millimeters.

[0084] During the rotation of the turbine, the straight blade receives ayawing moment around an axis oriented in a resistance direction(direction X), a pitching moment around an axis oriented in a transversedirection (direction Y), and a turning moment around an axis oriented ina lift direction (direction Z). Thus, the straight blade has to astrength enough for these moments. The tendency of Table 3 appears in awind turbine as well as a water turbine.

[0085] Table 4 shows an analysis of a relationship of a thickness of thestrut blade (symmetric blade) with a self starting performance, arotational resistance (efficiency decreasing factor), and a strength ofthe turbine, which was obtained from experiments and calculationsthereof. TABLE 4 Blade Thickness Starting Rotational (%) PerformanceResistance Strength  5 unacceptable small unaccetable 10 unacceptablesmall unaccetable 15 acceptable middle acceptable 20 acceptable middleacceptable 25 good large good 30 good large good 35 good large good 40good large good 45 good large good

[0086] The strut blade of Table 4 is the blade symmetric relative to ahorizontal line as shown in FIG. 3. The rotational resistance is a fluidresistance oriented in a direction of a wind or a water. A smallerthickness of the strut blade achieves a higher efficiency but decreasesthe strut blade in the self starting performance. The strut blade alsoreceives three moments as well as the straight blade.

[0087] From Table 4, a blade thickness more than 15% can be applied tothe strut blade to obtain an adequate starting performance of theturbine. A blade thickness selected between 15% and 20% has s middlerotational resistance but is best in view of the starting performance.Since the blade thickness selected between 15% and 20% achieves a middlestrength, the straight blade can be supported, for example, by a coupleof the strut blades to obtain a reliable strength.

[0088] For obtaining a better starting performance, a blade thicknessratio of 40% can be practical, although the rotational resistance islarge and the efficiency becomes smaller. The strut blade has a strengthhigher than the straight blade when the blade thickness is within alarger range. Because, the blade profiles are different from each otherand the strut blade has a configuration suitable for a gravity force. Ablade thickness of 5% to 10% is disadvantageous for the startingperformance and the strength but provides a smaller rotationalresistance. The strut blade having a blade thickness of 5% to 10% can beused if the number of strut blades are increased to achieve anappropriate strength of the turbine. The tendency of Table 4 appears ina wind turbine as well as a water turbine.

[0089] To summarize the above discussion, as understood from FIGS. 5 to10 and Tables 1 and 2, the solidity (NC/R) is preferably determined tobe not less than 0.5 for achieving a self starting performance of theturbine. The solidity between 0.65 and 1.2 is best. The solidity between0.5 and 2.2 can be practically used. However, the solidity between 0.1and 0.5 can be used to keep an acceptable efficiency of the turbine ifthe starting performance is compensated by a starting device.

[0090] As understood from FIG. 5, the blade angle of the straight bladebetween +1° and −1° or between +2° and −2° is best. A blade anglebetween +5° and −5° is practically used. A blade angle more than +5° orless than −5° is unpractical. FIG. 5 includes a view of the variation ofthe solidities, and the best or practical range of the blade angle canbe applied to each of the solidities described in FIG. 5.

[0091] From FIG. 6, the blade center of the straight blade is bestlocated at 25% from the fore end. A practical blade center is selectedbetween 15% and 40% in view of a self starting performance (a headfalling moment). The best or practical range of the blade center can beapplied to each of the solidities described above.

[0092] From Table 3, the straight blade thickness selected between 20%and 25% is most appropriate in view of the starting performance, theefficiency, and the strength of the turbine.

[0093] A preferable thickness may be selected between 20% and 30%. FromTable 4, the strut blade thickness selected between 15 and 20% is mostappropriate in view of the starting performance, the resistance, and thestrength.

[0094] Each factor of the blade angle, the blade center, the solidity,and the bade thickness may be separately determined. These factors maybe determined to be in conformity with each other.

[0095] For example, ten combinations of the five factors are as follows:

[0096] A blade angle between +5° and −5° or between +2° and −2° iscombined with a blade center of 25% or between 15% and 40%;

[0097] a blade angle between +5° and −5° or between +2° and −2° iscombined with a solidity between 0.5 and 2.2 or between 0.65 and 1.2;

[0098] a blade angle between +5° and −5° or between +2° and −2° iscombined with a straight blade thickness between 20% and 30; and

[0099] a blade angle between +5° and −5° or between +2° and −2° iscombined with a strut blade thickness between 15% and 20%.

[0100] Another combination of the three factors of the blade angle, theblade center, and the solidity may be possible as well as furtheranother combination of the four or five factors of the blade angle, theblade center, the solidity, the thicknesses of the straight blade andthe strut blade.

[0101] Particularly, the following combinations are preferable in viewof the efficiency and the self starting performance of the turbine. Suchcombinations are:

[0102] A blade angle between +2° and −2° is combined with a soliditybetween 0.65 and 1.2;

[0103] a blade center of 25% is combined with a solidity between 0.65and 1.2;

[0104] a solidity between 0.65 and 1.2 is combined with a straight bladethickness between 20% and 30%; and

[0105] a solidity between 0.65 and 1.2 is combined with a straight bladethickness between 20% and 30% and a strut blade thickness between 15%and 20%.

[0106] In place of the strut blades 4, a circular thin plate may beused. The upper and lower strut blades may be replaced by a singlecentral strut blade having a sufficient strength. The shaft 2 of thestraight blade type turbine 1 may be replaced by a pair of upper andlower short column bosses (not shown). The straight blade type turbinemay be mounted on a high side wall of a tall building with an axis ofthe turbine being horizontal. When the turbine is utilized as a waterturbine, each straight blade 3 is submerged into a water with an axis ofthe water turbine being vertical such that a free end of the waterturbine is oriented ahead. A submerged length of the straight blade 3may be changed according to an electricity generating quantity or astream speed of the water. The straight blade type turbine 1 is used notonly for an electricity generation but also for a heat converter and anenergy converter to lift a water. The present invention is also appliedto a manufacturing method of a straight blade type turbine.

[0107]FIGS. 11A, 11B, and 11C show the straight blade (main blade) 3which has a stream line convex 41 to reduce a rotational noise of thestraight blade type turbine 1. The convex 41 is defined in each of upperand lower edges of the straight blade (only an upper one is illustrated)with a longitudinal axis of the straight blade being vertical. Theconvex 41 is has a height H which is about a half of the maximumsectional thickness of the straight blade.

[0108]FIG. 11A is a top view (a reduced scale drawing of FIG. 2) of thestraight blade 3; FIG. 11B is a front view (in a rotation direction),and FIG. 11C is a side view. As illustrated in FIG. 11C, the convex 41has a profile which is an upper or lower half obtained by cutting theblade profile of FIG. 2 along the blade cord line 11. The convex 41 hasround head 42 symmetric relative to a vertical center line in the frontview of FIG. 11B. In FIG. 11B, the round head 42 is smoothly contiguouswith each side surface 43 of the straight blade 3. The profile of theconvex 41 is not limited in the shape of the straight blade 3.

[0109] As illustrated in FIGS. 11A and 11B, the round head 42 of theconvex 41 is a smooth curve shown in FIG. 11B between a fore end 44 anda middle of the convex 41. The round head 42 has a gradually decreasedthickness between the middle and a rear end 45 of the convex 41 as shownin FIG. 11A. The fore end 44 and the rear end 45 of the convex 41 aresmoothly contiguous to the fore edge 7 or a rear edge 8 of the straightblade. Preferably, the convex 41 is integrally formed with the straightblade 3 in use of the fabric material.

[0110] A ratio of the height H of the convex 41 to the cord length ispreferably between 12% and 17%, which is a half of the ratio between 24%and 34% applicable to the straight blade 3. Because, the straight bladehas a section generally symmetrical relative to a center line. Thispreferable range is based on an experimental data.

[0111] The convex 41 having the height ratio selected between 12% and17% eliminates an acoustic noise otherwise generated around the upperand lower ends of the straight blade which is used for a wind turbine.Because, the convex 41 can avoid eddies generated in a rear side of theupper or lower end of the straight blade. The convex 41 having theheight ratio selected between 12% and 17% eliminates a noise otherwisegenerated around the upper and lower ends of the straight blade which isused for a water turbine

[0112] In place of the blade-shaped convex 41, there may be provided aside plate (not shown) at each of upper and lower ends of the straightblade 3. Preferably, the side plate is a circular one which joins aplurality of straight blades 3 to each other in place of the strutblades 4. The side plate may be appropriately designed in shape.

[0113] The blade-like convex 41 and the side plate may be designedindependently or may be determined in combination with any of thefactors among the blade angle of FIG. 5, the blade center of FIG. 6, thesolidity of FIGS. 7 to 10 and Table 2, the straight blade thickness ofTable 3, and the strut blade thickness of Table 4.

What is claimed is:
 1. A straight blade type turbine having at least onetwo-dimensional blade positioned in parallel with and around a centralaxis of the turbine, characterized in that the two-dimensional blade hasa cross section with a blade cord turned around a center of thetwo-dimensional blade by an angle of 3° to −2° relative to a lineperpendicular to another imaginary line connecting the central axis withthe center of the two-dimensional blade; a distance between a fore endand the center of the cross section is 15 to 40 percent of a cord lengthof the blade; NC/R, which is calculated by a radius R extending from theaxis to the center of two-dimensional blade, the cord length C, and thenumber N of the two-dimensional blades, is between 0.5 and 2.2; and amaximum thickness of the two-dimensional blade is between 20 and 25percent of the cord length.
 2. The turbine according to claim 1characterized in that the turbine comprises a strut blade having asymmetric cross section joining the two-dimensional blade to a side ofthe central axis, the strut blade having a maximum thickness which isbetween 15 and 20 percent of a cord length of the strut blade.
 3. Astraight blade type turbine having at least one two-dimensional bladepositioned in parallel with and around a central axis of the turbine,characterized in that the two-dimensional blade is provided with astream line convex at a longitudinal end of the blade, the stream lineconvex having a thickness which is substantially a half of a maximumthickness of the two-dimensional blade.
 4. The turbine according toclaim 3 characterized in that the stream line convex has a thicknesswhich is between 12 and 17 percent of a cord length of the strut blade.5. The turbine according to claim 1 or 2 characterized in that thetwo-dimensional blade has the stream line convex described in claim 3 or4.